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Relationship between milk production and indicator traits of robustness in first-parity Holstein cows.

C. H. F. Zago Dias



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Relationship between milk production and indicator traits of robustness in first-parity Holstein cows.
C. H. F. Zago Dias*1, L. El Faro2, M. L. Santana Jr3, R. A. Teixeira1, A. A. Valotto4, L. T. Dias1. 1Universidade Federal do Paran� Curitiba, Paran�, Brazil, 2Instituto de Zootecnia Sert�ozinho, S�o Paulo, Brazil, 3Universidade Federal de Rondon�polis Rondon�polis, Mato Grosso, Brazil, 4Associa��o Paranaense dos Criadores de Bovino da Ra�a Holandesa Curitiba, Paran�, Brazil.

The current major challenges of dairy cattle improvement are to select animals with a greater capacity to overcome the metabolic disorders in postpartum. This study aimed to evaluate the association of the type traits angularity (ANG) and body conditions score (BCS) with test-day milk yield (TDMY) to identify more robust animals. In this study, 301,301 TDMY records from 33,543 first-parity Holstein cows, which belonged to 146 herds in the state of Paran�, Brazil, were analyzed. Angularity and BCS were classified at an average 88 d of lactation. A 2-trait random regression model between TDMY and the type traits was applied. The model included the fixed effects of contemporary group (herd, test-day year and month) and the linear and quadratic effects of cow age at calving and interval between classification date and calving (only for ANG and BCS) as covariates. The fixed lactation curve for TDMY was modeled using quadratic Legendre polynomials. For TDMY, additive genetic and animal permanent environmental effects were modeled as random effects using cubic Legendre polynomials, in addition to the residual effect. For ANG and BCS, only the additive genetic effects and residual were included as random effects. The (co)variance components were estimated by Bayesian inference using the GIBBS2F90 program (Misztal et al., 2002). The heritability for TDMY ranged from 0.22 to 0.36, with higher estimates close to peak yield. The heritability estimates for ANG and BCS were 0.17 � 0.03 and 0.19 � 0.02, respectively. Genetic correlations between TDMY and ANG or BCS were negative and antagonistic throughout lactation, with stronger correlations between TDMY and BCS at 30 d of lactation (−0.72) and between TDMY and ANG from 90 to 120 d (around −0.86). A higher genetic association was observed between BCS and TDMY at the beginning of lactation, a critical period when cows are in negative energy balance, while ANG showed a higher genetic association close to peak yield. Thus, the type traits studied may be used as auxiliary measures to identify more robust animals considering the different lactation periods.

Keywords: random regression model, transition period, type traits.

Biography: Degree in Animal Science, master's degree in Genetics and Animal Breeding from and a PhD in Animal Science. She is currently a scientific researcher at the Instituto de Zootecnia in Sert�ozinho, SP, Brazil and an accredited professor of the postgraduate course in Sustainable Animal Production, at the Instituto de Zootecnia. Has experience in Animal Genetic Improvement area, with an emphasis on Genetic Evaluation Methodologies for Milk Production, acting mainly on the following themes: new phenotypes, dairy cattle, quantitative genetics, components of variance, genetic evaluation and genetic parameters.